Machinery powered by electric motors or internal combustion engines (typically referred to as "prime movers") often use gears, shafts and the like to form a drive train providing power used to perform an end-use function. Automobiles, metal cutting and shaping machines, toggle-type presses and construction and earth-moving machines are but a few examples of such machinery.
As more specific examples, such machinery drive trains uses gears and shafts in speed reducers and right angle drives to reduce speed (from that of the motor or engine output shaft) and increase torque and/or to change the direction of power flow. Shafts interconnect "stages" of gearing or connect a final gearing stage to an output device such as automobile wheels, press head or, in the case of an earth-moving machine known as a walking dragline, to a "walk leg" drive.
In such machines, the drive train components (gears, shafts and the like) range in size from a few pounds to several thousand pounds. Clearly, small drive train components can be readily lifted, manually placed and positioned by one or two maintenance workers. Equally clear is the fact that assembly and maintenance personnel working with very large drive train components usually need auxiliary lifting equipment, a crane or the like, to help them lift, place and service such components.
To keep the machine functioning efficiently and in condition to satisfactorily perform its task, worn parts including drive shafts need to be serviced or replaced. However, with larger machines, maintenance and parts replacement can be an imposing challenge, especially if the parts are large and unwieldly. Nowhere is this more true than in large mobile machines such as earth-moving and earth-excavating machinery.
Such machinery is available in a wide variety of types ranging from the familiar rubber-tire mounted and crawler-mounted to the less-common dragline. A dragline is often used for removing top soil and "overburden" to expose a valuable mineral, e.g., coal, beneath but near the earth's surface.
Draglines are equipped with an angularly-extending boom from which is suspended a "bucket" having an open mouth and digging teeth, both toward the main portion of the machine. Overburden is removed by placing the bucket on the ground at a point distant from the machine and pulling it toward the machine, filling the bucket in the process. Once filled, the machine pivots about a central axis and the bucket emptied at a spoil pile somewhat away from the area being excavated.
Smaller draglines are crawler mounted much like a military tank and capable of movement in the same way albeit at much slower speeds. However, as draglines (and their digging buckets) increased in size, crawler mounting was found to be impractical and in the early 1900's, the "walking" dragline was developed. The walking dragline is so named because it takes short "steps" and uses a "walk leg" mechanism (which resembles a human leg) to do so. A difference is that in a walking dragline, both legs step simultaneously.
To give some perspective to the following discussion, a large walking dragline--made by Harnischfeger Industries of Milwaukee, Wis., and incorporating the invention--has a main housing portion (including the machinery deck, operator's cab and the like) which is about 105 feet long, about 80 feet wide, about 40 feet high and weighs about nine million pounds. The boom extends about 300 feet and the capacity of the digging bucket is about 80 cubic yards. The walk legs of such dragline take steps about seven feet in length.
At least because of its size, weight and complexity, several problems attend draglines of earlier configuration. One is that such machines are usually used in remote sites and replacement parts are difficult to deliver and, because of their size and weight, even more difficult to install. Another problem attends components, the weight of which is supported partly or entirely on a driving or driven shaft.
The walk leg assembly of a walking dragline is but one example in that a good portion of its weight is supported by the shaft which drives the assembly eccentric through engaged splines or the like. Sooner or later, it will become necessary to partially or fully withdraw the shaft for servicing the walk leg assembly or the shaft itself. When so doing, the shaft must be relieved of the weight of the assembly so that the frictional "drag" forces resisting withdrawal become very modest and the shaft can be more easily moved along its axis.
Heretofore, the technique for "unloading" the shaft involved using a crane or other lifting device to lift the assembly slightly upward. When a crane is used, it is a virtual necessity that the area above the assembly be open so that the lifting slings, hook or the like can be manipulated. But it is not unusual for the area above the assembly to be occupied by some sort of housing structure which must first be removed before crane attachment to the assembly can occur.
Wear cannot be avoided in any machine assembly having relatively moving parts. But the efforts of earlier designers in this field have not been entirely successful in reducing "downtime" of a machine which represents a very substantial capital investment. As an example, a walking dragline of the type described above represents an investment of in excess of $20,000,000. Its cost of operation may be in the range of $400 per hour. Clearly, even a minute of downtime is enormously expensive when measured against such cost of operation and lost production.
A method and related apparatus which dramatically eases the task of shaft withdrawal, which slashes downtime and which, as to the apparatus, is machine-mounted would be an important advance in the art.